The present invention relates to scroll machines. More particularly, the present invention relates to a scroll compressor which has a main bearing housing with an elastic center which is designed to coincide with the drive shaft""s nodal point corresponding to the first mode of vibration of the drive shaft.
A class of machines exists in the art generally known as scroll machines which are used for the displacement of various types of fluid. The scroll machines can be configured as an expander, a displacement engine, a pump, a compressor etc. and the features of the present invention are applicable to any one of these machines. For purposes of illustration, however, the disclosed embodiment is in the form of a hermetic refrigerant scroll compressor.
Scroll compressors are becoming more and more popular for use as compressors in both refrigeration as well as air conditioning applications due primarily to their capability for extremely efficient operation. Generally, these machines incorporate a pair of intermeshed spiral wraps, one of which is caused to orbit relative to the other so as to define one or more moving chambers which progressively decrease in size as they travel from an outer suction port toward a center discharge port. An electric motor is provided which operates to drive the orbiting scroll member via a suitable drive shaft affixed to the motor rotor. In a hermetic compressor, the bottom of the hermetic shell normally contains an oil sump for lubricating and cooling purposes.
The electric motor typically includes a motor stator which is press fit into a shell of the compressor. The drive shaft is typically press fit to the motor rotor and it is rotatably secured by a main bearing housing and a lower bearing housing. Each bearing housing is also secured to the shell of the compressor. During compressor operation, the drive shaft undergoes a nominal static deflection due to the net force on the drive shaft, and as a resultant dynamic load from various excitation sources. The inventors of the present invention have found that a major contribution to the sound levels of the operating compressor in the lower frequency bands is due to the vibration of the drive shaft.
The behavior of the drive shaft exhibits a nodal point (zero transverse displacement) in the vicinity of the main bearing of the main bearing housing. The kinetics of the drive shaft with respect to the main bearing of the main bearing housing suggest that the stress in the main bearing will be excessive, primarily because of the localized edge loading from the drive shaft. The localized edge loading is due in part to the rigidity of the main bearing housing which supports the main bearing. This excessive stress being induced in the main bearing due to edge loading can lead to excessive wear of the main bearing and eventually the bearing will wear out prematurely thus reducing the operational life of the compressor. In addition, the dynamic part of this load can be transmitted to the shell of the compressor and causes it to generate noise.
The present invention provides the art with a unique main bearing housing which is designed to locate the loaded drive shafts nodal point at the elastic center of the main bearing to eliminate edge loading and its associated problems. The main bearing housing of the present invention is designed to be compliant in the area supporting the main bearing which will locate the nodal point of the drive shaft closer to the elastic center of the main bearing. The compliancy in the mounting of the main bearing by the main bearing housing improves the drive shaft to main bearing contact distribution and further aids in the elimination of edge loading.